The present invention relates to vibration absorbers preferably used for vehicle wiper devices, and, more particularly, to vibration absorbers arranged between wiper frames and vehicle body frames.
As shown in FIG. 5, a wiper device 2 is typically provided along a lower side of a windshield 1 of a vehicle. The wiper device 2 has a pair of wiper arms 5, 6. A pair of wiper blades 3, 4 are secured to the distal ends, or ends spaced from a wiper frame 7, of the associated wiper arms 5, 6. Each wiper blade 3, 4 wipes a substantial area of an associated half of the windshield 1 with respect to the longitudinal middle of the windshield 1. The proximal ends, or bases, of the wiper arms 5, 6 are rotationally supported by associated shafts 8, 9. The shafts 8, 9 are secured to the wiper frame 7. A pair of movable levers 10, 11 are rotationally supported by the associated shafts 8, 9 at the bases, or proximal ends, of the levers 10, 11. In other words, the movable levers 10, 11 are connected to the associated wiper arms 5, 6 to rotate integrally with the wiper arms 5, 6 with respect to the associated shafts 8, 9.
A worm 13 is coupled with the output shaft of a motor 12 and meshes with a worm wheel 14. A base, or proximal end, of a drive lever 15 is secured to the center of the worm wheel 14. The distal end of the drive lever 15 is connected to the distal ends of the movable levers 10, 11 through associated link rods 16, 17.
When the motor 12 rotates the worm wheel 14 by means of the worm 13, the drive lever 15 is rotated to extend and retract the link rods 15, 16. Accordingly, the movable levers 10, 11 are rotated integrally with the associated wiper arms 5, 6 within a predetermined range around the associated shafts 8, 9. Every rotation cycle of the worm wheel 14 corresponds to one movement cycle of each wiper arm 5, 6. The movement cycle of the wiper arms 5, 6 is defined as proceeding from a lowermost position to an uppermost position and then returning to the lowermost position. While the wiper arms 5, 6 repeat their movement cycles, the wiper blades 3, 4 wipe corresponding portions of the windshield 1, as indicated by the double-dotted chain lines in FIG. 5.
When the link rods 16, 17 are extended and retracted, force acts on the wiper frame 7 through the shafts 8, 9 to vibrate the wiper frame 7. To counter this, a rubber vibration absorber 18 is deployed between the wiper frame 7 and the vehicle body frame when installing the wiper frame 7. The vibration absorber 18 prevents the vibration of the wiper frame 7 from being transmitted to the body frame. The vibration absorber 18 also absorbs vibration of the motor 12. In the wiper device 2 of FIG. 5, for example, four vibration absorbers 18 are provided at corresponding ends of the wiper frame 7.
FIG. 6 shows the structure of the vibration absorber 18. Specifically, the vibration absorber 18 has a cylinder 18b and a pair of substantially annular flanges 18c, 18d. The flanges 18c, 18d extend from near opposite axial ends of the cylinder 18b. The recess of the cylinder 18b is defined as a through hole 18a in which a cylindrical collar 20 is fitted. A bolt 21 is inserted in the collar 20. A washer 22 is fitted around the bolt 21. One axial end of the collar 20 abuts the washer 22. The other axial end of the collar 20 abuts a body frame 19. The vibration absorber 18 is fitted in an opening 7a extending in the wiper frame 7. The distal end of the bolt 21 is inserted in a hole 19a extending in the body frame 19. A nut 23 is fastened to the distal end of the bolt 21 to fasten the wiper frame 7 to the body frame 19.
One flange 18c is located between the wiper frame 7 and the washer 22 and has a pair of annular projections 18e, 18f. The projections 18e, 18f are located at a radial outer section of the flange 18c and project in opposite directions along the axis of the vibration absorber 18. One projection 18e abuts against the washer 22, and the other projection 18f abuts against the wiper frame 7. The other flange 18d is located between the wiper frame 7 and the body frame 19. The flange 18d is shaped as a mirror image of the flange 18c and has a pair of projections 18h, 18g. One projection 18g abuts against the body frame 19, and the other projection 18h abuts against the wiper frame 7.
An annular projection 18i is projected from the axial middle of the cylinder 18b and abuts against the wall of the opening 7a of the wiper frame 7. The projection 18i has a substantially semi-circular cross-sectional shape. A pair of annular projections 18j, 18k project from the inner side of the cylinder 18b at positions substantially corresponding to the flanges 18c, 18d. The projections 18j, 18k have a substantially triangular cross-sectional shape. The projections 18j, 18k abut against the collar 20. The projections 18j, 18k form a clearance A between the inner side of the cylinder 18b and the collar 20. The clearance A enables a portion of the cylinder 18b corresponding to the annular projection 18i to elastically deform in a radially inward direction.
The vibration absorber 18 absorbs a vibration component acting along axis Y of the wiper frame 7, or along the axis of the vibration absorber 18, through elastic deformation of the projections 18e to 18h. The vibration absorber 18 also absorbs a vibration component acting along axis X of the wiper frame 7, or in a radial direction of the vibration absorber 18, through elastic deformation of the projections 18i to 18k and by means of the clearance A.
The annular projections 18e to 18h are located coaxially with one another and define a uniform diameter with respect to the axis of the vibration absorber 18. In other words, the projections 18e to 18h are located along a line parallel to the axis of the vibration absorber 18. In this state, the projections 18e to 18h abut against the washer 22, the wiper frame 7, or the body frame 19 at positions spaced radially from the axis of the vibration absorber 18 by a uniform distance. Accordingly, vibration of the wiper frame 7 along axis Y is readily transmitted to the body frame 19 through the projections 18e to 18h. As described above, the vibration absorber 18 absorbs the vibration of the wiper frame 7 along axis Y only through elastic deformation of the projections 18e to 18h. Accordingly, the vibration absorbing performance of the vibration absorber 18 depends greatly on the hardness of the rubber forming the vibration absorber 18. However, it is difficult to optimize the vibration absorbing performance only by adjusting the rubber hardness of the vibration absorber 18. Furthermore, if the rubber hardness is decreased to improve the vibration absorbing performance, the wiper frame 7 is not reliably secured to the body frame 19.
The vibration absorbing performance of the vibration absorber 18 shown in FIG. 6 will hereafter be explained with reference to FIGS. 7(a) and 7(b). FIGS. 7(a) and 7(b) are graphs showing a rate at which the vibration of the wiper frame 7 is transmitted to the body frame 19 in the vicinity of the wiper frame 7. FIG. 7(a) shows the vibration transmission rate along axis Y of the wiper frame 7, and FIG. 7(b) shows the vibration transmission rate along axis X of the wiper frame 7. The natural frequency of the motor 12 shown in FIG. 5 is approximately 500 Hz, and its harmonic component is 1 kHz. As shown in FIG. 7(a), the vibration transmission rate is increased particularly for frequencies close to 1 kHz.
As shown in FIG. 7(b), the vibration transmission rate along axis X is decreased as compared to the vibration transmission rate along axis Y shown in FIG. 7(a). This is due to relatively small contact areas through which the projections 18i to 18k contact the wiper frame 7 or the collar 20. That is, elastic deformation of the projections 18i to 18k is relatively free.
However, when each wiper arm 5, 6 turns, or changes its moving directions at its uppermost position and its lowermost position, an increased force of inertia or reactive force acts on the wiper frame 7 along axis X. Since the projections 18i to 18k are relatively freely deformed as described, the projections 18i to 18k may be deformed excessively along axis X due to such force. This displaces the positions of the shafts 8, 9 secured to the wiper frame 7 with respect to the windshield 1. Accordingly, the portions of the windshield 1 wiped by the wiper blades 3, 4 are also displaced.
If the vibration absorber 18 is formed of relatively soft rubber, the vibration absorbing performance is improved. However, in this case, the vibration absorber 18 is further freely deformed along axis X due to the force of inertia or reactive force caused by the turning of the wiper arms 5, 6. Accordingly, the displaced amount of the positions of the shafts 8, 9 is further increased, so is the displaced amount of the portions of the windshield 1 wiped by the wiper blades 3, 4. In this case, the wiper blade 3, 4 may interfere with a pillar of the vehicle body frame when being moved by the associated wiper arms 5, 6.
To the contrary, if the vibration absorber 18 is formed of relatively hard rubber, the deformation of the vibration absorber 18 due to the force of inertia or reactive force caused by the turning of the wiper arms 5, 6 is suppressed. Thus, the vibration absorbing performance of the vibration absorber 18 is lowered.
As described, improving vibration absorbing performance and suppressing deformation of the vibration absorber 18 are not achieved at one time simply by adjusting the hardness of the vibration absorber 18.
FIG. 8 is a cross-sectional view showing another prior art vibration absorber 40. The vibration absorber 40 has an improved vibration absorbing performance regarding axis Y of the wiper frame 7, as compared to the vibration absorber 18 of FIG. 6. Same or like reference numerals are given to parts in FIG. 8 that are the same as or like corresponding parts in FIG. 6. As shown in FIG. 8, the annular projections 18f, 18h of the vibration absorber 40 are located radially outward from the annular projections 18e, 18g. In other words, the radial positions of the projections 18f, 18h are different from those of the projections 18e, 18g. This suppresses transmission of vibration acting along axis Y of the wiper frame 7 to the body frame 19 through the projections 18e to 18h. 
A clearance S1 between the flange 18c and the wiper frame 7 is located immediately below the projection 18e. Further, a clearance S2 between the flange 18d and the wiper frame 7 is located immediately above the projection 18g. Each clearance S1, S2 allows a portion of the associated flange 18c, 18d corresponding to the associated projection 18e, 18g to deform toward the wiper frame 7. This advantageously absorbs vibration of the wiper frame 7 along axis Y.
However, each flange 18c, 18d of the vibration absorber 40 defines a plane extending parallel to a plane perpendicular to the axis of the flange 18c, 18d. Thus, when the washer 22 or the body frame 19 applies force to the associated projection 18e, 18g along axis Y due to vibration of the wiper frame 7, the associated flange 18c, 18d deforms with respect to its radial inner section. Accordingly, most of the force applied to each projection 18e, 18g is received by the associated projection 18f, 18h, which is located at a radial outer section of the flange 18c, 18d. As a result, although improved as compared to the vibration absorber 18 of FIG. 6, vibration absorption along axis Y is still insufficient.
Furthermore, the portion of the vibration absorber 40 that absorbs vibration along axis X is configured exactly the same as that of the vibration absorber 18. Accordingly, regarding vibration along axis X, the vibration absorber 40 does not provide any improvement of both the vibration absorbing performance and suppressing of deformation of the vibration absorber 40.
Accordingly, it is an objective of the present invention to provide a vibration absorber preferably used for vehicle wiper devices and having improved vibration absorbing performance while suppressing unnecessary deformation of the vibration absorber.
To achieve the above objective, the present invention provides an elastic vibration absorber provided between a supported body and a support. The vibration absorber is fitted in an attachment opening formed in the supported body and is secured to the support with a securing member. The vibration absorber includes a cylinder and a pair of flanges. The cylinder is fitted in the attachment opening of the supported body and has a through hole through which the securing member is inserted. The flanges are provided near opposite axial ends of the cylinder to clamp the supported body. One flange is located between the supported body and a receiving surface provided for the securing member, the other flange is located between the supported body and the support. Each flange has an arched, axial cross-sectional shape.
The present invention also provides an elastic vibration absorber provided between a supported body and a support. The vibration absorber is fitted in an attachment opening formed in the supported body and is secured to the support with a securing member. The vibration absorber includes a cylinder having a through hole through which the securing member is inserted. An engaging portion is arranged around an axial middle portion of the cylinder and is fitted in the attachment opening. The engaging portion has an outer wall contacting a wall defining the attachment opening and an inner wall forming part of the through hole. A pair of contact surfaces are located at opposite axial ends of the cylinder. One contact surface contacts a receiving surface of the securing member and the other contacts the support. A pair of flanges are provided near the opposite axial ends of the cylinder to clamp the supported body. One flange is located between the supported body and the receiving surface of the securing member, and the other flange is located between the supported body and the support. A pair of thin portions are provided along the cylinder at positions corresponding to the opposite axial ends of the engaging portion for connecting the associated flanges to the engaging portion. A minimum radius defined by an outer periphery of each thin portion is smaller than a radius defined by a maximum outer diameter section of each contact surface.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.